Attachment magnético

7/28/2019 Attachment magntico

1/7

Corrosion resistance of ironplatinum magnets q

E.Y.L. Yiu a , D.T.S. Fang b , F.C.S. Chu b , T.W. Chow b, *

a Department of Health, Government of Hong Kong, Hong Kong, Chinab Faculty of Dentistry, The University of Hong Kong, 34 Hospital Road, Hong Kong, China

Received 17 June 2003; received in revised form 26 January 2004; accepted 3 February 2004

KEYWORDSCorrosion resistance;Ironplatinum;Neodymiumironboron;Magnets; Breakawayforce; pH

Summary Objectives . The objective of this study was to investigate the corrosionresistance of the prototype iron platinum (FePt) magnets and non-encapsulatedneodymiumironboron (NdFeB) magnets in three different pH environments.

Methods . The corrosion resistance of the magnets was studied using a corrosionindicator, the breakaway force. The breakaway forces of the magnets after immersionin three media, namely 1% lactic acid solution (pH 2.7), 0.1% sodium sulphidesolution (pH 12) and adjusted articial saliva (pH 6.8)were compared after 28 and60-day periods.

Results . By day 7, all NdFeB magnets dissolved completely in the acid medium, andthey showed signicantly lower breakaway forces at day 28 and day 60 in articialsaliva (90%, 69%) and in alkaline medium (67%, 42%). In contrast, the FePt magnets didnot show a drop in the breakaway forces after immersion in acid or articial saliva,although approximately half of the original breakaway forces were recorded at day 28and day 60 after immersion in strong alkali.

Conclusions . The new ironplatinum magnets, which require no yoke assembly orprotective casing, has good corrosion resistance for the oral environment. If itsretentive force can be improved without increasing its thickness (0.3 mm), then it willhave distinct advantages for clinical use.q 2004 Elsevier Ltd. All rights reserved.

Introduction

The development of intra-oral magnets remains achallenge for manufacturers despite their appli-cation in dentistry for more than 60 years. The rs tmagnet in dentistry can be dated back in 1941 1

when Freedman utilized curved magnets to improvethe stability of dentures for grossly resorbedmandibular alveolar ridges. In 1950, Behrman

implanted the rst Alnico V (aluminium ni ckel

cobalt alloy) magnet into human mandibles.2

Therst platinum cobalt magnet clinical trial wasconducted in 1952, and the material was reportedto have a maximum energy product, (BH)max ofapproximately 70 kJ m 2 3 , as compared to3.5 kJ m 2 3 for Alnico V. For a permanent magnet,it is the maximum energy product (BH)max, thatgives an indication of its power. The larger thisvalue, the greater the ux produced by a magnet ofa given volume, where B is the magnetic ux densitywhile H is the magnetic eld strength. 3 However,the size of the platinumcobalt magnet was too bigwhich limited its use. In 1967, the rst rare earthmagnets were produced. 4 They had many superior

0300-5712/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.jdent.2004.02.007

Journal of Dentistry (2004) 32 , 423429

www.intl.elsevierhealth.com/journals/jden

q This paper is based on an oral presentation given at the SixthInternational Symposium on Magnetic Dentistry 2002 atYokohama, Japan.

*Corresponding author. Tel.: 852-2859-0313; fax: 852-2547-0164.

E-mail address: [email protected] (T.W. Chow).
http://www.intl.elsevierhealth.com/journals/jdenhttp://www.intl.elsevierhealth.com/journals/jden


2/7

properties 5 and possessed strengths that were 2050 times greater per unit vol ume than the strongestferrite or Alnico magnets. 6 The rst generationalloy, SmCo, was made from the transitionalelementcobalt andthe rare earthelement samarium.Later in the 1970s, the second generation wasproduced from the transitional element iron andthe rare earth element neodymium. Boron, thethird element, was added to increase the funda-mental stability of the crystalline structure. 7,8 Thisalloy neodymiumiron boron (NdFeB) was 20 %stronger per unit volume than the SmCo alloy. 6

Magnetic attachments are commonly used inprosthodontics today and clinical successes inother el ds such as orthodontics, have also been

reported.912

Current magnetic systems consist of a magnet(NdFeB or SmCo) embedded inside a yoke cap, andan attachment keeper. The yoke cap of the magnetand the attachment keeper are usually fabricatedfrom magnetic stainless steel with soft magneticproperties. The cased magnet is housed insidethe prosthesis whereas the keeper is cemented tothe root of the abutment tooth or screwed onto theimplant.

One of the problems that limited their wideacceptance to clinicians was the low corro sionresistance of the permanent magnet alloy. 1318

Galvanic corrosion was another issue in this areawhereby the stainless steel was cast-bond ed or incontact with other types of dental alloys. 19,20 Thebulk of magnet that needed to occupy the denturespace was another clinical constraint.

Recently, a new alloy, Iron platinum (FePt)which is castable and has both soft and hardmagneti c properties, was introduced to dentis-try. 2124 As this alloy contains a large percentageof platinum, it was expected to have excellentcorrosion resistance. Hence, the possibility of thisnew FePt alloy as a replacement for NdFeB wasevaluated. The alloy was found to have a high-corrosion resistance when compared to the con-ventional magnetic stainless-steel keeper, and anincrease in the percentage of platinum by weightwould improv e its corrosion resistance in the oralenvironment. 25 The FePt alloy keeper also had highsaturation magnetization values and achiev ed greatattractive force with commercial magnets. 26

Intra-oral magnets of small dimensions aredistinctly advantageous for clinical use because alack of denture space is a common problem.However, a new prototype magnet using FePtalloy had been developed by Aichi Steel Works,Aichi-ken, Japan. The composition of this alloy is28.5wt%Fe71.5wt%Pt. The alloy is deposited on astainless-steel substrate by a sputtering process

(Fig. 1). The FePt magnet and AUM20 stainless-steelalternate on the surface, and appear as lines on theattracting face of the prototype magnet ( Fig. 2).They form magnetic circuits to yield strong reten-tion ( Fig. 2). As the magnet can be made to athickness of 0.3 mm, it will undoubtedly havepotential clinical advantages.

Although the magnetic properties of FePtalloy have been found to be comparable to thoseof rare earth magnets, 27 the corrosion resistance ofthe superthin magnet has not been investigated.The purpose of this study was to investigate thecorrosion resistance of this new FePt magnet.

Materials and methods

Two types of magnets were used in this study: thenon-encapsulatedmagnetizedNdFeBmagnetand thenon-encapsulated magnetized prototype iron-plati-num (FePt) magnet. The composition of the formerwas 63 wt%Fe26 wt%Nd6 wt%Dy and 5% others,with dimensions of 3.5 mm 1.5 mm 1 mm.

Figure 1 Sputtering lm deposition. (Courtesy of AichiSteel Works, Aichi-ken, Japan.)

Figure 2 Integrated structure of FePt magnet. (Cour-tesy of Aichi Steel Works, Aichi-ken, Japan.)

E.Y.L. Yiu et al.424


3/7

The composition of the latter was 28.5%Fe 71.5wt%Pt, with dimensions of 3.8 mm 2.8 mm 0.3mm.

Three corrosive media were used: 1% l ac tic acid,0.1% sodium sulphide and articial saliva 28 with pHvalues of 2.70 ^ 0.10, 12.00 ^ 0.05 and6.80 ^ 0.05, respectively. The relative degree ofacidity or alkalinity as measured by pH is one of thecharacteristics of corrosive environments. Sol-utions can be described as acidic, neutral, oralkaline according to the relative ratio of hydrogenions to hydroxyl ions. The three media wereselected for this study to represent the acidic,neutral and alkaline conditions. The acidic mediumwas introduced in this study because soft drinks

normally have a pH value of approximately 3. Thealkaline medium was selected, although it was notrealistic for the oral environment, to provideinformation on the corrosion resistance of magnetsas a function of pH. The articial saliva had anadjusted pH of 6.8, which represented a morerealistic environment. 29

Five samples of each type of magnet wereimmersed in the corrosive media, and a total of30 magnets were used.

Preparation of the keeper

A sheet of stainless-steel (Aichi Steel Works, Aichi-ken, Japan) with a composition of 19 wt%Cr 2wt%Mo 0.2 wt%Ti and around 80 wt%Fe wasprepared in dimensions of 32 mm 23 mm 1 mmand highly polished with a polishing machine (LunnMajor, Struners, Denmark), using various diamondparticles with sizes ranging from p220 to p1000, toproduce a perfectly at surface. Two screw holeswere drilled, one at each end of the keeper, and thekeeper was secured to the moving crosshead bymeans of two stainless-steel screws placed throughthe holes.

Preparation of the specimen

An acrylic resin holder was turned down from aproprietary clear acrylic rod and tted perfectlyinto the locking screw of the xed crosshead on theInstron testing machine. The cementing surface ofthe holder was particle abraded with 150 m m Al2O3particles, and conditioned with methyl methacry-late monomer (Unifast, Triad, GC Corporation,Tokyo, Japan) to achieve optimal bonding betweenthe magnet and the holder. A magnet was placedcentrally on the keeper with its attracting surfaceon the keeper. Panavia F cement (Kuraray, Osaka,Japan) was mixed according to the manufacturersinstructions, and placed on top of the magnet by

means of a small ball instrument. The crosshead(keeper) was moved up slowly at a speed of0.2 mm/min until the cement overowed slightlyas the top surface of the magnet just made contactwith the acrylic resin holder. The cement wasallowed to set completely at this position. Anadditional mix of Panavia F was used to cover theedges of the magnet and protect them from thecorrosive media. The procedures were repeated forall of the magnets.

Breakaway force measurement

An Instron testing machine (model 1185, Instron,High Wycombe, Bucks, UK) was used to record the

breakaway force between the magnet and thekeeper. A load cell with a 10 N full scale range(serial no. UK 511, model: 2518-808, Instron) wasused. The output was recorded by a built-in XYchart recorder with a tracing of force against timeon a millimeter grid chart paper. The magnet withits corresponding acrylic resin holder was rinsedunder distilled water for 5 s and dried underpressurized air for another 5 s. The attractivesurface of the magnet was further cleaned withethanol and cotton buds. The magnet and thekeeper specimen were mounted on the xed cross-head and moving crosshead, respectively ( Fig. 3).

The crosshead speed was set at 2 mm/min and thechart speed was set at 100:1 in proportion to thecrosshead displacement. The keeper was slowlymoved up until it just made contact with themagnet. The breakaway force was the maximumforce during the separation of the magnet and thekeeper when the keeper slowly moved away. Thebreakaway force measurement was repeated threetimes and the mean for each sample was used.

Immersion of magnets in different corrosivemedia

After the baseline measurement of breakawayforces, i.e. the day 0 reading, the magnets wereimmersed in three corrosive media (lactic acid,sodium sulphide and articial saliva) in individualcontainers. All corrosive media were pre-warmedto 37 ^ 1 8C and were changed every 7 days.Breakaway forces were measured under controlledambient conditions at a temperature of 23 ^ 1 8Cand a relative humidity at 70 ^ 5%.

Breakaway force measurement afterdifferent immersion periods

The magnets were removed from their respectivecorrosive media, rinsed, dried and cleaned prior

Corrosion resistance of ironplatinum magnets 425


4/7

to breakaway force measurement. The breakawayforce was measured at day 28 and day 60. Thedata were analysed using the ANOVA test and thepost hoc Tukey Kramer multiple comparisonstest. Paired t -tests were also conducted tocompare the performance of each type of magnetin each corrosive medium at day 28 and day 60.All tests were set at a statistical signicance ofP 0:05:

Results

Performance of non-encapsulated (bare)NdFeB magnets

The mean breakaway forces (as percentages of theoriginal values) and standard deviations (SD) in thethree corrosive media at days 0, 28 and 60 areshown in Table 1 and Fig. 4. By day 7, all themagnets were completely dissolved in 1% lactic acidand the breakaway force was 0. At day 28, thebreakaway forces had become 67 and 90% of theoriginal values in the alkaline and articial saliva,respectively, P , 0:05: At day 60, the breakawayforces dropped to 42 and 69% of the original valuesin the alkaline and articial saliva, respectivelyP , 0:05: Brownish corrosion products appearedon all attractive surfaces by day 60 for samples thatwere immersed in 0.1% sodium sulphide solution.The attractive surfaces of all the samples that wereimmersed in articial saliva had turned from silvergrey to yellow by day 60.

Performance of non-encapsulated FePtmagnets

The mean breakaway forces (as percentages of the

original values) and SD in the three corrosive mediaat days 0, 28 and 60 are shown in Fig. 5. At day 28,the breakaway forces were 100, 53 and 86% of theoriginal values in the acidic, alkaline and articialsaliva, respectively. At day 60, the breakawayforces were 90, 55 and 88% of the original value inthe acidic, alkaline and articial saliva, respect-ively. There were no statistically signicant differ-ences P , 0:05between the day-28 values and theday-0 values, or between the day-60 values and theday-0 values in either the acidic medium or articialsaliva. All of the attractive surfaces after immer-sion in the acidic medium and articial salivashowed no visible changes ( 10 magnication)at day 60. However, there was a statistically

Figure 3 Schematic diagram of assembly for measuringbreakaway force.

Table 1 Decrease of breakaway forces of NdFeB and FePt magnets after immersion in three corrosive media.

Corrosive media pH Decrease of breakaway force (%)

NdFeB magnets FePt magnets

Day 28 Day 60 Day 28 Day 60

Lactic acid 2.7 Dissolved** Dissolved** 100.5 (16.4) 90.1 (13.8)Articial saliva 6.8 89.6 p (8.9) 68.8* (4.3) 86.0 (22.8) 88.3 (29.2)Sodium sulphide 12 66.8* (7.4) 41.7* (6.0) 52.5* (8.1) 55.0* (10.1)

SD in brackets; * indicates a statistical difference P , 0:001:; ** magnets completely dissolved by day 7.



5/7

signicant differences P . 0:05 between the day-28 values and the day-0 values and between theday-60 reading and the day-0 reading in the alkalinemedium. Yellowish bands appeared on the attrac-tive surfaces of three samples that were immersedin the alkaline solution ( 10 magnication) after60 days (Fig. 6).

Discussion

Corrosion is difcult to measure and quantifyprecisely. Corrosion behaviour have been studiedin the past using advanced techniques such as theevaluation of pitting potential and galvanic cor-rosion, the utilization of anodic polarizationmeasurements and the identication of corrosionproducts, which requi red expensive equipment andcomplex techniques. 3032 Very few studies haveemployed the attractive force as a corrosionindicator. 32 This is probably due to the difcultiesencountered in orienting the magnet absolutelyparallel to the keeper. A decrease in the breakaway

force might be explained by a deterioration in theintegrity of the magnet surface or the magnet n otbeing orientated in a parallel plane to the keeper. 33

In this present study, the latter possibility wasexcluded by means of multiple statistical testswhich have demonstrated the excellent reliabilityof the experimental set-up P , 0:001: The changein the breakaway force as an indicator of thecorrosion process is therefore a simple, cost-effec-tive and reliable technique. Moreover, the change inretention force is more clinically relevant.

Theoretically, the retention force of unda-maged magnets should last innitively. However,

the corr osion of magnets leads to loss of reten-tion. 15,34 In the present study, the decrease of theattractive force in the articial saliva and the lossof non-encapsulated NdFeB magnets were com-parabl e to that found in an earlier laboratorystudy. 20 The brownish and yellowish productsfound on the surfaces of all non-capsulatedNdFeB after immersion in different media con-rmed that corrosion had taken place. These non-magnetic corrosion products might have preventedthe attractive surfaces of the magnet and thekeeper from coming into proximity, and theseparation led to the decrease of breakawayforce. In the acidic medium, the corrosion processprogressed rapidly, and the entire magnet dis-solved within 7 days.

For the non-encapsulated FePt magnets, thebreakaway force was maintained at around 90% ofthe original attractive force at day 60 in both 1%lactic acid and articial saliva. However, thepresence of yellowish bands on the attractivesurfaces of three samples, together with the dropofbreakawayforceto 55% of theinitial forceafter60days of immersionin 0.1% sodiumsulphidesuggestedsome corrosion of the FePt magnets in this medium.The excellent corrosion resistance of the magne-tized non-encapsulated FePt magnets in both theacidic and neutral media agreed with the ndings of

Figure 4 Decrease of breakaway forces (%) of the non-encapsulated NdFeB magnets

n 5.

Figure 6 Yellowish discoloration on a FePt magnet afterimmersion in alkaline solution for 60 days. (For interpret-ation of the references to colour in this gure legend, thereader is referred to the web version of this article).

Figure 5 Decrease of breakaway forces (%) of the non-encapsulated FePt magnets n 5.



6/7

non-magnetized FePt alloys. 25,35 This could bepartly explained by its high platinum content(71.5%by weight). Platinum possessesa high meltingpoint and high resistance to corrosion. It is notattacked by any single mineral acid, although it canbe dissolved in aqua-regia, and it does not oxidizewhen heated in air at 700 8C36 and it is considered asan inert metal. 37 Watanabe and co-workers 25

claimed that an increase in the Pt content mightimprove thecorrosion resistance in theoral environ-ment. Further investigations are needed in order toexplain its inferior corrosion resistance in the highlyalkaline medium. However, such high alkalinityhardly ever occurs in the oral environment andtherefore FePt magnets can be expected to exhibit

excellent corrosion resistance clinically.Permanent magnets that are based on interme-tallic compounds of rare earth elements and tran-sition metals exhibit exceptionally advantageousmagnetic properties. These include one of the mostwidely used magnets in dentistrythe neodymiumironboron magnets. However, as conrmed in thisstudy, the use of such magnets is severely limited bytheir poor corrosion resistance in various environ-ments. The manufacturer (Aichi Steel Works, Aichi-ken, Japan) claims that it has solved the corrosionproblem by employing a stainless-steel yoke andcreating a perfect seal between the magnet andyoke cap with microlaser-welding technique. Com-mercial products such as the MagFit system that aremanufactured with this technique supposedly haveexcellent corrosion resistance. In a simulated oralenvironment, the newly invented ironplatinummagnet designed for intra-oral applications, whichrequires no yoke assembly or casing, has muchimproved corrosion resistance compared withNdFeB magnet. If the retentive force ( , 0.3 N) canbe improved without increasing its thickness(0.3 mm), then it will certainly have distinct advan-tages for clinical use, as a lack of denture space is acommon intra-oral problem.

The present ndings suggest that the prototypesuperthin magnet exhibits good corrosion resis-tance and has important potential clinicalapplications.

Conclusions

The following conclusions, based on the 60-dayexperimental period, can be drawn from this study:

1. The non-encapsulated NdFeB magnet has poorcorrosion resistance in articial saliva, 1% lacticacid and 0.1% sodium sulphide.

2. The non-encapsulated prototype FePt magnethas improved corrosion resistance compared toNdFeB in both articial saliva and 1% lactic acid.

Acknowledgements

The authors thank Aichi Steel Corporation, Aichi-ken, Japan for the supply of prototype ironplatinum magnets and neodymiumiron boronmagnets. Thanks also goes to our technical assist-ant, Miss S.W. Cheng for the illustrations.

References1. Freedman H. Magnetic counter-inuence in full lower

denture retention. Dental Digest 1941; 47 :498503.2. Behrman SJ. The implantation of magnets in the jaw to aid

denture retention. Journal of Prosthetic Dentistry 1960;10 :80741.

3. Riley MA, Walmsley AD, Harris IR. Magnets in prostheticdentistry. Journal of Prosthetic Dentistry 2001; 86 :13742.

4. Becker JJ, Luborsky FE, Martin DL. Permanent magnetmaterials. Institute of Electrical and Electronics EngineersTransactions on Magnetics 1968; 4 :8499.

5. Tsutsui H, Kinouchi Y, Sasaki H, Shiota M, Ushita T. Studieson the Sm-Co magnet as a dental material. Journal of DentalResearch 1979;58 :1597606.

6. Jackson TR.The application of rare earth magnetic retentionto osseointegrated implants. International Journal of Oraland Maxillofacial Implants 1986; 1 :8192.

7. Sagawa M, Furimura S, Togowa N, Yamatoto H, Matsura Y.New material for permanent magnets on a base of Nd and Fe. Journal of Applied Physics 1984; 55 :20837.

8. Croat JJ, Herbst JF, Lee RW, Pinkerton FE. PtFe and NdFe-based materials: a new class of high-performancepermanent magnets (invited). Journal of Applied Physics1984; 55 :207882.

9. Blechman AM. Magnetic force systems in orthodontics. American Journal of Orthodontics 1985; 74 :20110.

10. Gilling BRD. Magnetic retention for overdentures. Part I. Journal of Prosthetic Dentistry 1981; 45 :48491.

11. Gilling BRD. Magnetic retention for overdentures. Part II.

Journal of Prosthetic Dentistry 1983; 49 :60718.12. Frederick DR. A magnetically retained interim maxillary

obturator. Journal of Prosthetic Dentistry 1976;36 :6713.13. Drago CJ. Tarnish and corrosion with the use of intraoral

magnets. Journal of Prosthetic Dentistry 1991;66 :53640.14. Riley MA, Williams AH, Speight JD, Walmsley AD, Harris IR.

Investigations into the failure of dental magnets. Inter-national Journal of Prosthodontics 1999; 12 :24954.

15. Walmsley AD, Frame JW. Implant supported overdentures-the Birmingham experience. Journal of Dentistry 1997; 25 :S437.

16. Davis DM, Packer ME. Mandibular overdentures stabilized byAstra Tech implants with either ball attachments ormagnets: 5-year results. International Journal of Prostho-dontics 1999; 12 :2229.

17. Naert I, Gizani S, Vuylsteke M, Steenberghe DV. A 5-yearprospective randomized clinical trial on the inuence ofsplinted and unsplinted oral implants retaining a mandibular



7/7

overdenture: prosthetic aspects and patient satisfaction. Journal of Oral Rehabilitation 1999; 26 :195202.

18. Chan MFWY, Johnston C, Howell RA, Cawood JI. Prosthetic

management of the atrophic mandible using endosseousimplants and overdentures: a six year review. British Dental Journal 1995; 179 :32937.

19. Imuro F, Yoneyama T, Okuno O. Corrosion of coupled metalsin a dental magnetic attachment system. Dental Materials Journal 1993; 12 :13644.

20. Kitsugi A, Okuno O, Nakano T, Hamanaka H, Kuroda T. Thecorrosion behavior of Nd 2Fe14 B and SmCo5 magnets. DentalMaterials Journal 1992; 11 :11929.

21. Tanaka Y, Watanabe I, Udoh K, Atsuta M, Hisatsune K,Nakano M, et al. Relations between micro- and magnetic-structures and magnetic properties of FePt ferromagneticalloys. Journal of the Japanese Society for Dental Materialand Devices 1998;1744.

22. Watanabe K, Masumoto H. On the high energyproduct of FePt permanent magnet alloys. Journal of Japan Institution onMetals 1983;47 :699703.

23. Watanabe K. Permanent magnet properties in FePtNbsystem alloys. Journal of Japan Institution on Metals 1990;54 :128490.

24. Watanabe K. Permanent magnet properties and theirtemperature dependence in the FePtNb alloy system.Materials Transactions JIM 1991;32 :2928.

25. Watanabe I, Hai K, Tanaka Y, Hisatsune K, Atsuta M. In vitrocorrosion behavior of cast iron-platinum magnetic alloys.Dental Materials 2001;17 :21720.

26. Watanabe I, Tanaka Y, Fukunaga H, Hisatsune K, Atsuta M.Attractive force of castable iron-platinum magnetic alloys.Dental Materials 2001;17 :197200.

27. Nakamuru O. Magnetics-fundamentals and application .Tokyo: Corona; 1999.

28. Leung VWH, Darvell BW. Calcium phosphate system in saliva-

like media. Journal of the Chemistry Society, Faraday Transactions 1991;87 :175964.

29. Humphrey SP, Williamson RT. A review of saliva: normalcomposition, ow, and function. Journal of ProstheticDentistry 2001;85 :1629.

30. Gurrappa I. Suitability of NdFeB permanent magnets forbiomedical applications-a corrosion study. Journal of Alloysand Compounds 2002; 339 :2417.

31. Obatake RM, Collard SM, Martin J, Ladd GD. The effects ofsodium uoride and stannous uoride on the surface rough-ness of intraoral magnet systems. Journal of ProstheticDentistry 1991;66 :5538.

32. Kitsugi A, Okuno O, Nakano T, Hamanaka H, Kuroda T. Thecorrosion behavior of Nd 2Fe14 B and SmCo5 Magnets. DentalMaterials Journal 1992;11 :11929.

33. Lewandowski JA, White KC, Moore D, Johnson C. Aninvestigation of two rare earth magnetic systems bymeasuring grip force and reseating force. Journal of Prosthetic Dentistry 1988;60 :70511.

34. Davis DM. Implant supported overdenturesthe Kingsexperience. Journal of Dentistry 1997;25 :S337.

35. Haoka K, Kanno T, Takada Y, Kimura K, Okuno O. Corrosionresistance of the PtFeNb magnets for dental-casting.Dental Materials Journal 2000; 19 :27082.

36. Hartley FR. The chemistry of platinum and palladium .London: Applied Science Publishers Ltd; 1973.

37. Davies JR. Corrosionunderstanding the basics. ASM Inter-national w USA First printing; January 2000.


Documents

Attachment magnético